A print head for use in an impact printer such as a wire printer is disclosed in, for example, Japanese Patent Laid-Open No. 11615/1978, where the number of driving arms is equal to the number of print elements such as wires. The arms have the same length respectively and are arranged radially. The arms are actuated by electromagnetic driver devices having coil cores that are aranged on a circle. Therefore, the number of component parts of the print head increase.
In an attempt to reduce the number of component parts, an improved pint head has been proposed in Japanese Patent Laid-Open No. 154178/1980, where driving arms are fabricated as one unit. In particular, the arms are frmed of a single rolled metal by a press working so that the arms are connected together at their outer ends like a ring. However, all of the arms have the same shape and the same dimensions, and are actuated by electromagnetic driver devices having coil cores arranged on a same circle similarly to the aforementioned known print head.
It should be noted that the rolled metal has a different Young's modulus by changing a dirction to the direction of rolling. For this reason, the arms of the latter-mentioned print head differ in Young's modulus respectively and so they vary in natural frequency and produce different resilient forces. Therefore, the arms respond at different rates. As a result, the head may form incorrect dots or may print at various pressure. Variations in response do not pose serious problems in printers of the type where the print speed is about 100 characters per second or less. However, the variations in response affect materially the print quality in high-speed printers whose print speed is about 200 characters per second or in ultra high-speed printers whose print speed is about 400 characters per second.